为什么此arraylist中的索引超出范围错误？

Question

Why does this code cause an index out of bounds error?

ArrayList<Integer> list2 = new ArrayList<Integer>();

for (int i = 1; i <= 10; i++){
    list2.add(i); //adding numbers to arraylist.  Length is equal to 10
}
int size = list2.size(); //size now equals 10

for (int i = 0; i < size; i++)
    if (list2.get(i) == 3 || list2.get(i) == 4)
    list2.remove(i);
System.out.println(list2);

Answer 1

The first size is 10 , but when you remove an element, it becomes 9, so when the index i gets to 9 you can't access the box 9 has it does not exists (as index starts at 0 )

---

You need to get the current size at each iteration as you're modifying it

for (int i = 0; i < list2.size(); i++) {
    if (list2.get(i) == 3 || list2.get(i) == 4) {
        list2.remove(i);
    }
}
//[1, 2, 4, 5, 6, 7, 8, 9, 10]

Also the 4 is not deleted, why ?

• Because when you check index 2 you find the value 3 so you remove it,
• then all the values go down in the list, the value 4 is not at index 2 ,
• as i will be now 3 you won't check that box

---

To remove both 3 and 4 you can use one of the following solution:

• list2.removeIf(i -> i == 3 || i == 4);
• list2 = list2.stream() .filter(i -> i != 3 && i != 4) .collect(Collectors.toCollection(ArrayList::new));